Added fonts suporting new xscreensaver dialoguebox and added lubuntu-grub-theme.

Summary: Added xfonts-efont-unicode which is needed for new xscreensaver dialogue box and lubuntu-grub-theme so that it gets installed by default.

Test Plan:
Check that xscreensaver loads without any warnings.

	   Check if lubuntu-grub-theme gets installed and selected by default on new installations.

Reviewers: kc2bez, wxl, tsimonq2

Reviewed By: wxl

Differential Revision: https://phab.lubuntu.me/D66